From the teachings of the Rebbe on the Torah portion
This week's Torah portion, Chayei Sara, tells us about the mission upon which Abraham sent Eliezer his servant, and the oath he made Eliezer take beforehand. Enjoining him to find the proper wife for his son Isaac, Abraham tells Eliezer: "Put, I pray you, your hand under my thigh." Customarily, when a person takes an oath, he must hold something holy upon which he swears. This is why Abraham told Eliezer to place his hand under his thigh, for Abraham had performed the mitzva of circumcision when he was ninety-nine years old.
Some perplexing questions arise from Abraham's behavior. According to our Sages, the patriarchs performed the mitzvot even before we received the Torah. Did Abraham, then, have nothing else upon which to ask Eliezer to swear, other than the mitzva of circumcision? And, if Abraham already followed the laws of the Torah, why did he wait until G-d personally commanded him to circumcise himself at such an advanced age?
Chasidic philosophy explains that there is a great difference between mitzvot performed before the Torah was given and after. Prior to the Revelation, mitzvot--even those performed by our ancestors--did not have the power to bring holiness into the world. Physical reality was unchanged by the performance of a mitzva, and the physical objects that were used remained in their former state. There was an unbridgeable gap between the spiritual and physical realms. The power to combine the spiritual and the physical was only given to the Jewish people after the Torah was revealed on Mount Sinai. Since that time, when a Jew performs a mitzva with a physical object, that object is elevated and becomes holy.
No matter how refined a person may be, he is limited in his ability to imbue the physical with G-dliness. But, since we do mitzvot with the power given to us by G-d and the strength that comes from His commandments the physical world is elevated by our actions.
The only mitzva Abraham performed as a direct command from G-d was circumcision. Thus, this mitzva carried the power of G-d's command. This explains why Abraham waited so long to circumcise himself. He wanted to perform the mitzva in such a manner that his body would acquire holiness. Because the circumcision was done in response to a direct command from G-d, Abraham was given the opportunity to make his flesh holy.
This mitzva, therefore, was the only one which Abraham could possibly ask Eliezer to swear on for any other physical article he had used in his life to perform mitzvot did not have the same holiness.
